Preservation of rubber



Patented Oct. 1, 1940 UNITED STATES PRESERVATION or RUBBER,

Robert L. Sibley, Nitro, W. Va., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware v.

No Drawing. Original application March 9, 1935, Serial No. 10,175. Divided'and this application November 23, 1936, Serial No. 112,345 a I 11 Claims. (o1. 260 s02) The present invention relates to the art of rubber manufacture, and particularly relates to the preparation of rubber compounds which resist deterioration due to the effects of heat 5 and/or oxygen. It has long been known that such deterioration can be retarded to a certain degree by treating the rubber eitherbefore or after vulcanization with certain substances known as age-resisters or antioxidants. One object of the invention is to provide a superior class of antioxidants for rubber. A" further object of this invention is to provide a class of materials which, when incorporated into rubber, preferably before the vulcanization thereof, imparts thereto properties markedly resistant to tear and cracking when portions thereof have been repeatedly and alternately stretched and the tension removed. Such a process is analogous to the flexing of an automobile tire in actual service.

The age resisting characteristics of a vulcanized rubber product can be readily ascertained by subjecting portions of the vulcanized product in a bomb to the action of 300 pounds of oxygen per square inch at a temperature of 70 C.

The aged rubber samples are then examined and tested and the test data compared with the unaged rubber samples. The deterioration in properties effected as a result of the oxidation.

treatment is indicative of the result that would normally be expected of that particular stock during actual service. Such a test is known as the Bierer-Davis aging test and produces an efiect on a vulcanized rubber stock comparable with that resulting from several years of natural aging of the rubber depending on 'the test. Alternatively, the age resisting characteristics of 1 a vulcanized rubber product can be readily ascertained by subjecting portions of the vulcanized product to a constantly renewed stream of air 40 in the Geer oven maintained at a temperature aromatic primary amine and a ketone or derivative thereof in conjunction with a diaryl p-phenylene diamine as an adjuvant thereto whereby a rubber product possessing improved flexing and aging propertieslis obtained.

As specific examples of the reaction product of an aromatic primary amine and a ketone are I the reaction product oraeetone and aniline, reaction product of acetone and beta naphthylamine, reaction product of para phenetidine and acetone, reaction product of diacetone al-" cohol and aniline, reaction product of acetone and para amino diphenyl, the reaction product. of methyl ethyl ketone and aniline; and equiva .lents and analogues thereof, which materials are.

obtainable by heating said reactants under pressure at a temperature of substantially 180 C. to* 200 C. in the presence of a suitable catalyst or condensing agent; Where convenient or desirable othermetho'ds Well known to those skilled in the art may be employed. As a further example of a ketone-aromatic primary amine re-' action product included as one component of the preferred mixed antioxidant and flexing. agent according to the present invention, substantially 100 parts by weight of a product formed by reacting acetone and aniline, comprising 2,2,4- trimethyl-dihydroquinoline (see' Reddelien and Thurm, Berichte der deutschen chemischen Gesellschaft, vol. 65, pages 1511-1521-4932), were treated with parts by weight of concentrated hydrochloric acid and heated therewith for20 hours at a-temperature of substantially to C. The crystalline salt-like product first produced changes to an amorphous mass, which on cooling formed a brittle solid. The material so formed, being acid in'nature, was preferably neutralized. before being incorporated in rubber. The product after neutralization melted at substantially to C. Other quantities of hydrochloric acid may be employed in the preparation of this class or ketone-aromatic, primary amine reaction products. Thus, 100 parts by weight of'2,'2,4-tri"- f m'ethyl-dihydroquinoline has been treated with 10, 15, 25 and 30 parts by weight of concentrated: hydrochloric acid in the manner analogous to that described above wherein'55 parts by weight of acid were employed. Further, other than concentrated acids may be employed. Thus,-I- may employ a dilute acidpas for example dilute hydrochloric acid. Again other'acids may be,5o

employed. Thus, I may employ sulphuric acid. As examples of diaryl p-phenylene diamines comprising the second component of the preferred class of antioxidants and flexing agents are diphenyl p-phenylene diamine, ditolyl p-phenylene diamine, dibeta naphthyl p-phenylene diamine and analogues and equivalents thereof.

after vulcanization.

As a specific embodiment of the invention but not as a limitation of the scope thereof rubber stocks were compounded as follows:

renders it, when employed alone as an antioxidant, unfitted for commercial application.

Other ratios of a diaryl p-phenylene diamine, for example diphenyl p-phenylene diamine, and the hydrochloric acid treated 2,2,4-trimethy1- dihydro-quinoline have been employed in typical rubber stocks, and the resulting vulcanized rubber products found to possess improved flexing properties as well as improved solubility of diphenyl p-phenylene diamine in rubber. Thus, among other ratios, 0.2, 0.3 and 0.5 parts of diphenyl p-phenylene diamine have been employed mixture of diphenyl p-phenylene diamine and the hydrochloric acid treated 2,2,4-trimethyldihydro-quinoline was found by actual test to Withstand 25% more fiexings than the stock containing the hydrochloric acid treated 2,2,4-trimethyl-dihydro-quinoline alone. Portions of the above unaged vulcanized rubber stocks were artificially aged in the Geer oven for 3 and 5 days respectively and then'flexed in the manner described above. Here again the stocks containing the preferred mixed antioxidant were found to flex markedly better than the stocks containing'the hydrochloric acid treated 2,2,4-trimethyldih'ydro-quinoline alone. The preferred mixed antioxidant was found also to possess desirable solubility in the rubber mix. Diphenyl-pphenylene diamine, when employed alone as an antioxidant in the above stock exhibits very poor solubility; and blooms or migrates to the surface of the vulcanized product within a few hours This undesirable property Stock A Stock B in conjunction with 0.8, 0.7 and 0.5 parts of 2,2,4- parts b parts b trimethyl-dihydro-quino1ine.

Welght weght As a further example of the use of the preferred class of antioxidants rubber stocks were gfig rubber 0 gg compounded comprising Stock 0 Stock D Steane acid 3 3 parts by parts by Benzothlazylthiobenzoat 0. 8 0. 8 Diphenylguanidine. 0. 2 o. 2 weght weght g fi m pg g 4 y 1'00 01108.0 I63. 6 time y dilwdw-quinofine M %?r%ti?t ct ff??f::33333333333313: g8 23 Zinc oxide 5 5 Sulfur s 3 The rubber stocks were vulcanized and the 3 e g g vulcanized rubber aged in the oxygen bomb at a igggiihbg1iiggig 1 0,8 8 temperature of 70 C. andunder a pressure of g g gg g gge 00 pounds f o y en per square Inch with the Reaction product of acetone nausea following result; naphthylamine 1.0 0.6

s Table I The rubber stocks so compounded were vulcan- Oure Modulusof ized and the cured rubber product aged in the e c ty Tensfle toxygen bomb at a temperature of 70 C. and a Stock lbs /in at break e1 [1 Minsaged elongation of il 2 5 5 pressure .of 300 pounds of oxygen per square inch, piessure 0 and the results obtained as given in Table II.

' 75 so 0 2080 4300 520 Table H 75 so 96 1895 2850 450 a as .2 as is an o 1976 4360 530 Cure P1 9 Tensile 90 30 96 2020 2705 415 Hrs elastlcltym at break Ult. 90 30 0 2030 4290 530 Stock d lbs/in. at in elong., 90 30 96 2100 2765 410 Mins Steam elonzgagm of lbs'lin? percent I pressure 0 An examination of the modulus and tensile C 75 30 o 1988 4050 565 figures contained in the above Table I shows that 75 3 12 1690 2310 440 stock B containing the mixed antioxidant ac- 38 8 i333 cording to the invention is materially better in 90 30 0 1995 4020 540 age resistance than stock A containing the hy- 38 8 drochloric acid treated 2,2,4-trimethyl-dihydro- 90 so 120 1975 2370 385 quinoline alone. Moreover, When portions of the 2g g i838 unaged rubber stocks were flexed in the manner 30 o 2080 3875 500 hereinbefore set forth, the stock containing the 105 1945 The above data in Table II shows that the mixed antioxidant of the present invention possesses superior antioxidant properties to that of the reaction product of acetone and beta naphthylamine alone. Flexing tests, carried out in the manner described above on the unaged cured rubber stocks and on the same unaged stocks after ageing for 3 and 5 days in the Geer oven at 70 C., showedstock D containing the mixed antioxidant to be markedly superior to stock C containing the acetone-beta naphthylamine reaction product alone as the antioxidant. The mixture of diphenyl p-phenylene diamine and the acetone-beta naphthylamine also was readily soluble in the rubber mix and did not exhibit any blooming or migration of antioxidant to the surface of the vulcanized rubber as does diphenyl p-phenylene diamine when employed alone in typical tread stocks.

As a furtherexample of the use of the improved antioxidant of the present invention rubber stocks where compounded comprising The stocks so compounded were vulcanized and the cured'rubber product aged in the oxygen bomb at a temperature of 70 C. and an oxygen pressure of 300 pounds per square inch with the following result:

Table III Cure Modulus of H elasticity in 5 E; Ult. Stock Lbs a d lbs/in." at in along,

Mins stemii g elongation of lbs fin 2 percent pressure 300% i i A comparison of the test data given in Table III above shows a marked improvement in the antioxidant action of the acetone-p-phenetidine reaction product when employed in conjunction with smaller amounts of a diaryl p-phenylene diamine, for example diphenyl p-phenylene diamine. Flexing tests carried out on the unaged vulcanized rubber stock and also on the same stock after aging for 3 and 5 days in the Geer oven at 70 C. showed in all cases a marked improvement in resistance to flex cracking of those stocks containing the acetone-p-phenetidine reaction product activated by diphenyl p-phenylene diamine over those stocks containing the acetone-p-phenetidine reaction product alone. Furthermore, the mixture of the acetone-p-phenetidine reaction product and diphenyl p-phenylene diamine possesses desirable rubber solubility, whereas, as stated above, diphenyl p-phenylene diamine, when employed alone, does not.

As a further specific embodiment of the present invention rubber stocks were compounded com- The compounded rubber stocks were vulcanized by heating in a press for 60, '75, 90 and 105 minutes at 130 pounds of steam =pressureper square inch and portions of the cured rubber product. flexed unaged and after. aging for. 3 days in the Geeroven at 70C; The results ofthe flexing tests showed the rubber stock containing the mixture of the acetone-aniline reaction product and diphenyl p-phenylene diamine to be far more resistant to flex cracking'than the stock containing the ketone-amine product alone. Furthermore, saidmixed antioxidant-was found to be rubber soluble. i i I From rthe specificlexamples hereinbefore set forth, it is shown that rubber compositions containing small proportions of the preferred class of materials markedly resist the deterioration influences due to heat, oxidation and flexing.

Obviously, practice of the present invention is not limited to the specific compositions given above, such compositions being merely illustrative of the manner of employing the antioxidants or age-resisters of this invention. The antioxidantsor age-resisters may be employed inconjunction: with other vulcanizing agents than those specifically disclosed, for this invention is applicable generally to pure rubber or rubber compositions of the most varied nature. ,Furthermore, the preferred class of materials may be employed in rubber stocks in conjunction with other accelerators than the ones specifically shown with varying differences in tensile and modulus proper-- ties but still exhibiting the desirable qualities of the class.

It is understood that the term treating as employed in the appended claims is used in a generic sense to include either the incorporating of the preferred class of materials into the rubber by milling or similar process, or their addition to the rubber latex before its coagulation, or to the application thereof to the surface of a mass of crude or vulcanized rubber. The term rubber is likewise employed in the claims in a generic sense to include caoutchouc, whether natural or synthetic, reclaimed rubber, balata, gutta percha, rubber isomers and like products whether or not admixed with fillers, pigments or accelerating agents.

The present invention is limited solely by the claims attached hereto as part of the present specification.

The present application is a division of application Serial No. 10,175, filed March 9, 1935, now U. S. Patent 2,100,998.

What is claimed is:

1. The method of preserving rubber which comprises treating rubber with a mixture of a diaryl p-phenylene diamine' and at least an equal proportion by weight of a reaction product of an aromatic primary amine and an aliphatic ketone obtained by condensing the said reactants in the presence of a condensation catalyst.

2. The method of preserving rubber which comprises treating rubber with a mixture of a diaryl p-phenylene diamine and at least an equal proportion by weight of a reaction product of an amino diphenyl and a ketone obtained by condensing the said reactants in the presence of a condensation catalyst.

3. The method of preserving rubber which comprises treating rubber with a mixture of a diaryl p-phenylene diamine and at least an equal proportion by weight of a reaction pro-duct of para amino diphenyl and an aliphatic ketone obtained by condensing the said reactants in the presence of a condensation catalyst.

4. The method of preserving rubber which comprises treating rubber, with 'a mixture of a diaryl p-phenylene diamine and at least an equal proportion by weight of a reaction product of para amino diphenyl and acetone obtained by condensing the said reactants in the presence of a condensation catalyst.

5. The method of preserving rubber which comprises treating rubber with a mixture of diphenyl p-phenylene diamine and at least an equal proportion by weight of a reaction product of para amino diphenyl and acetone obtained by condensing the said reactants in the presence of a condensation catalyst.

6. The method of preserving rubber which comprises treating rubber with a mixture of diphenyl p-phenylene diarnine and at least an equal proportion by weight of a reaction product of para phenetidine and acetone. obtained by condensing the said reactants in the presence of a condensation catalyst.

7. The method of preserving rubber which comprises treating rubber with a mixture of diphenyl p-phenylene diamine and at least an equal proportion by weight of a reaction product of acetone and beta naphthylamine obtained by condensing the said reactants in the presence of a condensation product.

8. A composition comprising rubber and a mixture of a diaryl p-phenylene diamine and at least an equal proportion by weight of a reaction product of an amino diphenyl and 9.

keton'e obtainedby condensing the said reactants in the presence of a condensation catalyst.

9. A composition comprising rubber and a mixture of a diaryl p-phenylene diamine and at least an equal proportion by weight of a reaction product of para amino diphenyl and an aliphatic ketone obtained by condensing the said reactants in the presence of a condensation catalyst.

10. The method of preserving rubber which comprises treating rubber with a mixture of a diaryl p-phenylene diamine and at least an equal proportion by weight of a reaction product of an aliphatic ketone containing less than '7 carbon atoms and an aromatic amine selected from the group consisting of aniline, para phenetidine, beta naphthylamine and para amino diphenyl obtained by condensing the said reactants in the presence of a condensation catalyst.

11. A composition comprising rubber and a mixture of a diaryl p-phenylene diamine and at least an equal proportion by weight of a reaction product of an aliphatic ketone containing less than 7 carbon atomsand an aromatic amine selected from the group consisting of aniline, para phenetidine, beta naphthylamine and para amino diphenyl obtained by condensing thevsaid reactants in the presence of a condensation catalyst.

ROBERT L. SIBLEY. 

